1. Field of the Invention
The present invention relates to a driving force distribution control device for a vehicle which controls engaging force of a coupling mechanism so as to change transmission torque, and distributes driving force.
2. Description of the Related Art
Conventionally, with a driving force transmission system for four-wheel-drive vehicles and so forth, a system has been known wherein a coupling mechanism made up of a multiple disc clutch and the like is disposed within a transfer, and controlling engaging torque of this coupling mechanism continuously controls distribution of driving force toward the rear wheel side.
With such a system, a torque limiter for limiting engaging torque of the coupling mechanism is provided. For example, Japanese Patent No. 2,599,965 discloses art wherein, with a four-wheel-drive vehicle having a center differential for dividing driving force output from the engine so as to transmit the divided force to a front-wheel-drive system and a rear-wheel-drive system, a mechanical torque limiter is disposed on the rear-wheel-drive system (or the front-wheel-drive system), and while this torque limiter is running, limiting differential of the center differential enables jack-rabbit starts and rapid acceleration.
However, the conventional torque limiter fixes the transmission torque at a constant value, so in the event of mounting nonstandard-diameter tires or in the event of performing specific control in a state wherein oil temperature of the differential (especially the rear differential) rises abnormally, deterioration of driving performance is brought about, and also in the event of transition from an ordinary control state to a specific control state or in the event of switching of the control state at recovery from the specific control state to the ordinary control state, the engaging torque is drastically changed, thereby causing problems such as deterioration for driving stability and driving performance.